Attempt to fix mypy failure on ci

[vfdev-5]

Fixed failing job "Lint / python-types / linux-job" : https://github.com/pytorch/vision/actions/runs/6955317152/job/18923844284?pr=8128

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/vision/8128

• 📄 Preview Python docs built from this PR

Note: Links to docs will display an error until the docs builds have been completed.

❌ 6 New Failures, 6 Unrelated Failures

As of commit 9ba6f6c with merge base 893b4ab ():

NEW FAILURES - The following jobs have failed:

• Tests / unittests-linux (3.10, linux.12xlarge, cpu) / linux-job (gh)
• Tests / unittests-linux (3.8, linux.12xlarge, cpu) / linux-job (gh)
• Tests / unittests-macos (3.10, macos-12) / macos-job (gh)
• Tests / unittests-macos (3.11, macos-12) / macos-job (gh)
• Tests / unittests-macos (3.8, macos-12) / macos-job (gh)
• Tests / unittests-macos (3.9, macos-12) / macos-job (gh)

FLAKY - The following jobs failed but were likely due to flakiness present on trunk:

• Tests / unittests-macos (3.8, macos-m1-12) / macos-job (gh)
• Tests / unittests-windows (3.10, windows.4xlarge, cpu) / windows-job (gh)
• Tests / unittests-windows (3.11, windows.4xlarge, cpu) / windows-job (gh)
• Tests / unittests-windows (3.8, windows.4xlarge, cpu) / windows-job (gh)
• Tests / unittests-windows (3.9, windows.4xlarge, cpu) / windows-job (gh)

BROKEN TRUNK - The following job failed but were present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• Tests / unittests-linux (3.9, linux.12xlarge, cpu) / linux-job (gh)

This comment was automatically generated by Dr. CI and updates every 15 minutes.

[NicolasHug]

Thanks for fixing this @vfdev-5

Would it work to just write this line unconditionally?

If there's no cleaner why to please mypy here, I'd suggest to stop type-checking this part of the code-base. It's not worth wasting time on.

[vfdev-5]

I'm not sure if we can write it in single line...

Technically, mypy is right as root arg is Optional[str], so self.root type is Optional[str]. In subclasses we are passing root string, but self.root inherits the original type: Optional[str].

we can force the cast as (+/- some type ignores)

self.root: str = root

but this wont be correct.

Alternatively, as you say we can stop type checking this code and all related subclasses...

[vfdev-5]

Just seen that this PR is on the origin of this problem: #8124

[pmeier]

Superseded by #8134.